1. Technical Field
The present embodiment relates to a packaged device in which a device chip such as a micro movable element is sealed, and a method of manufacturing the packaged device.
2. Background of the Art
In recent years, elements or devices having micro structures formed utilizing MEMS (Micro-ElectroMechanical Systems) techniques have been applied in various technical fields. These devices include micro movable elements having micro movable portions, for example, micro mirrors, angular speed sensors, and acceleration sensors. The micro mirror is utilized in the fields of, for example, optical disk techniques and optical communication techniques as a device providing a light reflecting function. The angular speed sensor and the acceleration sensor are utilized for various applications; for example, these sensors are used to provide a hand jiggling preventing function for video cameras or cellular phones with cameras and used for car navigation systems, air bag open timing systems, and posture control systems for cars, robots, or the like. The micro movable element is described in, for example, Japanese Patent Laid-Open Nos. 2003-19700, 2004-341364, and 2006-72252.
The micro movable element comprises, for example, a movable portion that is, for example, swingable, a fixed portion, a coupling portion that couples the movable portion and the fixed portion together, and a driving electrode pair that drives the movable portion. A package in which a device chip with such a micro movable element formed sealed therein needs to maintain the amount of moisture in an internal space in which the micro movable element or the device chip is accommodated, at a given value or less (for example, at most 5,000 ppm). A large amount of moisture in the internal space may induce discharging in the vicinity of a driving electrode for the micro movable element. The induced discharging may degrade the electrical or driving characteristics of the element. A small amount of moisture is contained in or attached to the package member or the device chip. The moisture evaporates to the internal space to increase the amount of moisture in the internal space, which may exceed an allowable level.
Moisture absorbents exerting a chemical or physical moisture absorbing effect are conventionally used in order to maintain the amount of moisture in the internal space in the package at a low level. For example, a paste-like moisture absorbent is applied to a predetermined position in the internal space in the package and then dried. The moisture absorbent is thus provided in the internal space together with the device chip.
However, to make the moisture absorbent available, it is necessary to provide not only a device chip mounting area but also an arrangement area for the moisture absorbent. The size of the arrangement area tends to increase consistently with the amount of moisture absorbent. Thus, the use of the moisture absorbent is not preferable for a reduction in package size. Furthermore, the moisture absorbing effect of the moisture absorbent is likely to be temporally degraded. This makes it difficult to reliably keep the amount of moisture in the internal space at a low level.